Interactions of hearing aid compression release time and fitting formula: effects on speech acoustics

The effects of the interaction of compression release time and prescribed gain on running speech processed through a hearing aid on KEMAR was investigated. A digital instrument was programmed to fit a mild to moderate sloping hearing loss using probe microphone measures to reach targets prescribed by NAL-NL1, DSL I/O, FIG.6 or ASA2p with release times of 40 and 640 ms for each condition. Recordings were made through KEMAR and analyzed to determine the long-term-average-speech spectra, consonant-to-vowel ratios and the RMS amplitude of 32 phonemic units. Aided and unaided results were compared. Within each prescriptive formula, changes in release time affected all of the speech measures subsequent to programming the instrument to a static-composite signal. The short release-time condition produced the greatest alteration to the speech signal. Release time may need consideration when fitting hearing aids to target gain prescriptions.